A Functional Magnetic Resonance Imaging Study Of Patients With TMJ Synovitis Pain

Objective: Temporomandibular disorders(TMD)are considered the most common cause of chronic orofacial pain except odontalgia.The central nervous system(CNS)mechanism has recently been hypothesized to initiate or contribute to the development of TMD related pain.In the present study,we tested this hypothesis by investigating the regional homogeneity(Re Ho)and functional connectivity(FC)of pain-related brain regions in TMD pain patients using resting-state functional magnetic resonance imaging(rs-f MRI)and analyzing the relationship of clinical pain intensity and spontaneous brain activities.Method: Psychophysical data(SCL-90)of 10 female temporomandibular joint(TMJ)synovitis patients with unilateral open-mouth pain and 10 age-matched healthy controls(HC)were collected and compared between groups using independent sample t-tests.Pain intensity of the TMD patients in the open-mouth state was measured by Visual Analogue Scale(VAS).First,the changes in Re Ho during mouth-open session relative to mouth-closed session were compared between TMD patients and healthy controls.Second,the identified brain area with abnormal Re Ho served as the seed region and its FC with the rest of the brain were further examined.Results:1.Two TMD patients were later confirmed to have TMJ synovial chondromatosis,and thus were discarded from further analysis.8 TMJ synovitis patients and 10 HCs were finally recruited in the present study.2.For the psychological results,after correcting for multiple comparisons,TMD still showed significantly higher scores in the subscales of Somatization,Interpersonal sensitivity and Depression.3.For the f MRI results,two clear patterns of the FC maps were revealed in both conditions and both groups: the r AI were positively correlated with the salience network(SN)related brain areas and negatively correlated with the DMN related brain areas.4.For results of comparisons between groups,compared with the HCs,TMD patients showed decreased Re Ho in the right anterior insula(r AI)which further showed showed a weaker positive FC with the left mid-cingulate cortex(MCC)and a weaker negative FC with the right precuneus/posterior cingulate cortex(PCC)in TMD pain patients compared with HCs.5.Furthermore,the r AI-MCC FC showed a negative correlation with the pain intensity: the higher the pain intensity,the weaker the FC between the r AI and the MCC was in patients.Conclusion:1.Our findings reveal that TMD pain is associated with disrupted synchronization of local neural activities in the r AI,known to be a key region in the salience network(SN)and involved in pain processing.2.Importantly,the observed abnormal FCs of the rAI with the MCC and PCC suggest a functional maladaptive plastic changes of connectivities within the SN and between the SN and the DMN.3.To be a consistently nociceptive input,TMD chronic pain may cause a increased sensitivity of central nociceptive system,such as abnormal neural activities in certain brain area or functional connectivities between key nodes of brain networks,indicating the key role that central sensitivity plays in TMD pain.4.The route through which the central neural system may contribute to the development or maintenance of TMD pain may be related to inherent personality-related psychological factors that may reduce the brain’s capacity to modulate nociceptive input.